A credible and serious presidential candidate from one of the major political parties -- in fact, his party's current frontrunner -- feels the need to make a public declaration that he will be faithful to his marriage vows. It's a fair assumption that he has done so not to get closer to God, but because he thinks the stunt could get him one step closer to the White House. And, given that this candidate has twice before broken his marriage vows, when you think about it, what he's really saying is that he promises to be more faithful to voters than he was to his first two wives.

The best that you can hope for from presidential campaigns is that they're empowering, enlightening, and engaging. Sadly, with this detour into fidelity pledges, the current Republican contest has gone right to embarrassing.

As a presidential candidate, Newt Gingrich has been fairly unflappable. He can take a punch, and hit back twice as hard -- usually in the same news cycle. He stands his ground in debates, even when he's being fired upon from all directions.

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And yet, now, apparently, something has rattled Gingrich: the possibility that his well-publicized marital shortcomings could undermine his appeal in a conservative state like Iowa.

Think of it this way: Republicans want to beat Obama. They just don't want the drama. And so Gingrich's opponents have made it their mission to stir up that very thing -- focusing on the former House speaker's personal life.

It began with a holier-than-thou ad from Mitt Romney highlighting that Romney, the perennial second-place finisher has been -- gee whiz! -- married to the same woman for 42 years. The message to voters: Gingrich hasn't.

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Then came last week's debate in Iowa, where several of Gingrich's opponents piled on the family-values bandwagon. Or is that a station wagon? Picking up on the theme that Romney had laid out, one White House hopeful after another proudly recited his or her own marital resumes. It was uncomfortable to watch, as if you had all these people claiming to be morally superior to everyone else.

Who talks that way? Most of us know we're sinners and that we fall short, yet here you have a batch of candidates peddling perfection -- all because they see it as a way of attacking the frontrunner, who is undeniably imperfect. In the process, we learn nothing about the candidates.

Respectfully, Gingrich is wrong. This subject is not fair game. Whether someone has been faithful to his or her spouse is a private and sometimes painful matter that shouldn't be a chew toy in the political arena. It is simply none of the voters' business. Once a person becomes president, you could argue that his fidelity, or lack thereof, matters -- but not before.

You'll sometimes hear the line that Rick Perry used at the debate -- about how if you'll cheat on your spouse, then you'll cheat on your business partner or in other aspects of your life.

Really? There is simply no connection between being a good husband and being a good president. Democrats still look back on Bill Clinton as having a successful presidency, despite his indiscretions. And they look at George W. Bush as having a failed presidency despite the fact he was apparently faithful to his wife.

At the debate, Gingrich concluded his remarks with this: "In my case, I've said up-front openly I've made mistakes at times. I've had to go to God for forgiveness. I've had to seek reconciliation. But I'm also a 68-year-old grandfather. And I think people have to measure who I am now and whether I'm a person they can trust."

I have no idea whether Gingrich is someone we can trust. And I'm more than happy to see his opponents attack him on matters of policy, temperament or judgment. That's fair game. But marital fidelity should be off-limits.

Gingrich needs to stop conceding so much on this issue. He needs to get off defense and go back on offense. In fact, if I were Gingrich, the next time this issue is raised, I'd turn to my opponents and say:

"Yes, I'm made mistakes. I'm not perfect. My earlier marriages were failures. Let's do this. Everyone who is flawless and who has a perfect marriage and who has never made a mistake in life can vote for you. Everyone else can vote for me. And we'll see how it goes."